This case-control study will test the hypothesis that dietary vitamin A may be protective against the development of lung cancer. We will take advantage of the multiethnic population of Hawaii, with its dietary heterogeneity, to interview 500 newly-diagnosed patients with primary lung cancer. These patients will be identified through the seven major hospitals on Oahu and will be men and women of Japanese, Caucasian, Filipino, Chinese and Hawaiian ethnic groups. For each lung cancer patient, two age- and sex-matched controls will be identified using the random-digit dialing method. Both cases and controls will be interviewed in their homes by trained multi-lingual interviewers, using a questionnaire designed to elicit quantitative information on the consumption of a large number of dietary items containing preformed vitamin A and vitamin A precursors. A detailed smoking history and history of exposure to occupational lung carcinogens will also be part of the questionnaire. The data will be analysed to determine the dietary vitamin A consumption of cases and controls with adjustment for smoking and occupational history. Further analysis will determine the dietary vitamin A consumption of cigarette-smoking cases versus cigarette-smoking controls with adjustment for covariates. The demonstration of a relatively low dietary vitamin A intake among lung cancer patients, particularly among those who are smokers, would suggest that the incidence of this very common cancer might be reduced by increases in vitamin A intake.